Study Confirms Maurepas Swamp, Marshes Dying for Lack of Fresh Water

Newswise — Without a diversion from the Mississippi River or the introduction of other sources of fresh water in the near future, the Maurepas Swamp in southeast Louisiana will continue on a clear path toward becoming marsh and open water, a new study by Southeastern Louisiana University biologists and other scientists confirms.

Writing in the Journal of Coastal Research, Gary P. Shaffer, Southeastern professor of biological sciences, notes that the Maurepas Swamp complex, the second largest coastal forest in Louisiana, has been radically reduced over the years due to excessive logging, development, changing water levels, nutrient deprivation and saltwater intrusion. The paper was co-authored with several other scientists from Southeastern and LSU.

“Much of the remaining swamp is in a severe state of deterioration,” Shaffer said.

He explained that the establishment of levees over the last century along the Mississippi River to eliminate natural flooding removed a once reliable source of fresh water, sediments and nutrients that swamps require for healthy growth.

“This has enabled salt water from the Gulf of Mexico to make further inland intrusions,” he said. “Combined with rising sea levels and the construction of massive canals, such as the Mississippi River Gulf Outlet (MRGO), the intensity and frequency of saltwater intrusions has only grown worse. Consequently, most of the Maurepas Swamp appears to be in transition to marsh and open water.”

The scientists’ findings are based on comparisons of selected groupings of sites in the southern wetlands of Lake Maurepas. The sites had three different levels of water quality: including stagnant and nearly permanently flooded areas, sites with severe saltwater intrusion, and sites that receive some freshwater runoff. Salinity levels appeared to be the major factor causing sites to rapidly deteriorate, with the most degraded areas located near Lake Pontchartrain or along the margin of Lake Maurepas.

“The Maurepas Swamp is in a steady state of rapid decline, and that’s evident by the loss of much of the baldcypress and water tupelo forests that were a mainstay of the swamp,” Shaffer said. “Over the past seven years, nearly 20 percent of the original 1,860 trees in our study plots have died.”

A Mississippi River diversion – under study for several years now by the Environmental Protection Agency and scientists at Southeastern and LSU – would decrease the salinity, increase the levels of nutrients, and provide much needed sediment necessary to rebuild the subsiding swamp, Shaffer explained.

“It is likely that the influences of freshening would be felt in wetlands as distant as Lake Pontchartrain,” he said. “Even the smallest proposed diversion would replace all of the water in Lake Maurepas twice each year and it can only exit to Lake Pontchartrain through Pass Manchac and North Pass.”

Mississippi River reintroductions have been considered at Violet, Bonnet Carre, La Branch and two in the Maurepas Swamp, Shaffer said

The study also evaluated the region following the 2005 hurricanes, with the scientists concluding that the extensive lateral root systems of baldcypress and water tupelo can hold an entire ecosystem together, while also serving as valuable natural storm buffers.

“If we want to reverse the decline of coastal Louisiana swamps, we have to find and use sources of fresh water that currently are being wasted, including water from the Mississippi River, as well as treated sewage effluent,” he said. “The proper freshening of the region should enable restoration of the swamps in the Lake Pontchartrain Basin.”

Co-authors of the study included Thais E. Perkins, William B. Wood and Jason Zoller of Southeastern; Susan S. Hoeppner of the LSU Department of Oceanography and Coastal Science; and Demetra Kandalepas of the LSU Department of Biological Sciences. Shaffer also credited the efforts of numerous undergraduate and graduate students who performed much of the field work.